i have set up three 5 gallons for shrimp,snails and fry.i have had one set up for about a month and a half and when i need to change the water the mulm on the bottom flies around everywhere and smells really bad like i didn't even do a water change.how do you vac it out without sucking up the fry,snails and shrimp?i really need to know as this smells like rotten eggs.Even as we speak i have the window open toa ir it out bleh